1. Field of the Invention
The invention relates to an engine cooling system that cools an engine by circulating coolant through the inside of the engine.
2. Description of Related Art
In a liquid-cooled engine, the engine is cooled by circulating coolant between the inside of the engine and a radiator with the use of a pump. Conventionally, as described in Japanese Patent Application Publication No. 2015-010577 (JP 2015-010577 A), there is such a cooling system for a liquid-cooled engine, in which a coolant circuit through which coolant is circulated branches off into a plurality of routes outside the engine, the plurality of routes including a radiator route that passes through a radiator, and a multi-way valve is provided at the branched position of those routes so as to be able to vary the flow rate ratio of coolant flowing into the routes. Such an engine cooling system is able to adjust the cooling capacity of the cooling system as needed in response to an operating condition of the engine. For example, before completion of warm-up of the engine, the cooling capacity of the cooling system is allowed to be decreased by the multi-way valve being controlled such that the flow rate of coolant passing through the radiator reduces, with the result that warm-up of the engine is facilitated. For example, when the amount of heat generated from the engine is large, the cooling capacity of the cooling system is allowed to be increased by the multi-way valve being controlled such that the flow rate of coolant passing through the radiator increases.
Incidentally, in an engine cooling system including a multi-way valve as described above, if the total flow rate of coolant passing through the multi-way valve is continuously smaller than the coolant discharge amount of the pump, the pressure of coolant at a portion upstream of the multi-way valve in the coolant circuit may excessively increase. For this reason, in such an engine cooling system, any portion of the coolant circuit is required to have a high pressure resistance in consideration of an increase in pressure in such a case, so higher pressure-resistant and more expensive components are required. This leads to an increase in manufacturing cost.